Preparation Of Nanofiltration Membranes Research Articles

Masking covalent organic frameworks (COFs) with loose polyamide networks for precise nanofiltration

Covalent organic frameworks (COFs) with uniform, tunable nanoporosities are promising alternatives to prepare nanofiltration membranes with homogeneous nanochannels for high-resolution molecular sieving. Due to the poor membrane-forming ability as well as the relatively inadequate strategies for pore engineering, thus far, the preparation of continuous and defect-free COF membranes with tunable pore sizes is still challenging. Herein, we demonstrate an ingenious strategy to prepare the heterostructured membranes featuring the loose polyamide networks masked COF nanofilms for precise sieving of small molecules. The loosely structured polyamides are created by the interfacial polymerization to mask the chemically stitched (chemically interlinked) ultrathin COF nanosheets. The masked polyamide with flexible, loose networks not only enhance the membrane-forming ability of the natively rigid ultrathin COF nanofilms, but also provide a masking effect that can effectively tune the pore size of the heterostructured COF membranes. Benefitting from the synergistic enhancement of the membrane-forming ability and the pore size tunability, thus-prepared membranes exhibit excellent molecular sieving performances toward various small molecules. This work is expected to provide a guidance for the rational design and controllable preparation of COF membranes for precise nanofiltration.

Interfacial polymerization nanofiltration membrane with visible light photocatalytic self-cleaning performance by incorporation of CQD/TiO2

• Photocatalytic CQD/TiO 2 -mediated nanofiltration membrane was prepared via interfacial polymerization. • The prepared membrane has excellent separation performance for dye wastewater treatment. • The membrane exhibits efficient and stable visible light-driven self cleaning ability. Integration photocatalysis with membrane technology offers a potential solution to combat fouling dilemma. Herein, an interfacial polymerization polyamide nanofiltration (NF) membrane with self-cleaning ability was prepared by incorporation of carbon quantum dots /titanium dioxide (CQD/TiO 2 ) nanoparticles (NPs). The addition of hydrophilic CQD/TiO 2 NPs promoted membrane hydrophilicity and endowed the NF membrane with high water flux (67.22 L m −2 h −1 ), which was 1.8 times compared with that of the pristine membrane, and salt rejection of Na 2 SO 4 (96.7%). Simultaneously, the prepared NF membranes maintained high dye rejection to methyl blue (MYB, 99.1%) and congo red (99.8%). Moreover, visible light-driven photocatalytic ability of CQD/TiO 2 allowed the membranes to efficiently degrade MYB dyes absorbed on the membrane surface. In stark contrast to the results of cyclic physical water cleaning, the flux recovery ratios were maintained 97–98% without sacrificing MYB rejections during the cyclic fouling-irradiation process, demonstrating stable and efficient self-cleaning performance. Even after continuous membrane fouling for 72 h, the water flux only decreased by 6.7% after visible light irradiation, surpassing the performance of pristine polyamide NF membrane (decreased by 23.4%). The hydrophilicity and visible light-driven self-cleaning ability make the prepared NF membrane via interfacial polymerization highly suitable for efficient dye wastewater treatment.

A new strategy to accelerate co-deposition of plant polyphenol and amine for fabrication of antibacterial nanofiltration membranes by in-situ grown Ag nanoparticles

Due to the far cheaper price than polydopamine, plant polyphenol and amine have been widely used for mussel-inspired chemistry. However, co-deposition of them still suffers the problem of long co-deposition time owning to the slow dissolution and diffusion of oxygen in solution. Herein, we reported an interesting strategy regarding addition of AgNO3 as both oxidant and Ag precursor into co-deposition of tannic acid and diethylenetriamine for nanofiltration (NF) membrane preparation. It was found that, AgNO3 addition not only shortened co-deposition time, but also in-situ generated Ag nanoparticles and rendered membrane surface antibacterial activity. The effect of AgNO3 addition on co-deposition behavior, physicochemical properties, separation and antibacterial performance of the as-prepared NF membrane were systematically investigated. The results showed that, when 0.15 wt% AgNO3 was added, the prepared NF membrane possessed a pure water flux of 5.36 L m−2h−1 bar−1, a MgCl2 rejection of 86.5% and an excellent antibacterial activity. This study not only provided a facile and effective strategy to prepare antibacterial NF membrane, but also offered new insights into co-deposition of polyphenol and amine for more widespread applications.

Tuning the nano-porosity and nano-morphology of nano-filtration (NF) membranes: Divalent metal nitrates modulated inter-facial polymerization

Divalent metal nitrates were pre-loaded on polysulfone support to modulate the interfacial polymerization between piperazine (PIP) and trimesoyl chloride (TMC). It is found that the nano-porosity and nano-morphology of thus formed thin film composite polyamide (TFC-PA) nano-filtration (NF) membranes as well as their filtration performance could be effectively tuned by the type and concentration of the divalent metal salts, especially the divalent cations used. Main group cations, such as Mg (II) and Ca (II), increased the water flux of the NF membranes by increasing their surface nano-scale nodular arrays without altering the pore sizes and rejections of the membranes, while transitional metal cations such as Zn (II), Cu (II) and Co (II) increased the water flux of the NF membranes not only by the formation of high surface area nano-scale Turing type crisscrossed ridge networks, but also by the increase of their nano-pore sizes due to their coordination with the >NH groups of the PIP. The prepared NF membranes pore sizes adjustable from 0.54 Å to 0.90 Å could be developed to have varied selectivity and rejections among inorganic salts and organic dyes.

γ-Valerolactone as Bio-Based Solvent for Nanofiltration Membrane Preparation.

γ-Valerolactone (GVL) was selected as a renewable green solvent to prepare membranes via the process of phase inversion. Water and ethanol were screened as sustainable non-solvents to prepare membranes for nanofiltration (NF). Scanning electron microscopy was applied to check the membrane morphology, while aqueous rose Bengal (RB) and magnesium sulphate (MgSO4) feed solutions were used to screen performance. Cellulose acetate (CA), polyimide (PI), cellulose triacetate (CTA), polyethersulfone (PES) and polysulfone (PSU) membranes were fine-tuned as materials for preparation of NF-membranes, either by selecting a suitable non-solvent for phase inversion or by increasing the polymer concentration in the casting solution. The best membranes were prepared with CTA in GVL using water as non-solvent: with increasing CTA concentration (10 wt% to 17.5 wt%) in the casting solution, permeance decreased from 15.9 to 5.5 L/m2·h·bar while RB rejection remained higher than 94%. The polymer solubilities in GVL were rationalized using Hansen solubility parameters, while membrane performances and morphologies were linked to viscosity measurements and cloudpoint determination of the casting solutions to better understand the kinetic and thermodynamic aspects of the phase inversion process.

Effect of Solution Viscosity on the Precipitation of PSaMA in Aqueous Phase Separation-Based Membrane Formation.

Aqueous phase separation (APS) is a recently developed sustainable alternative to the conventional organic solvent based nonsolvent-induced phase separation (NIPS) method to prepare polymeric membranes. In APS, polyelectrolytes are precipitated from aqueous solutions through pH or salinity switches. Although APS differs from NIPS in the polymer and solvents, they share many tuning parameters. In this work, we investigate the APS-based preparation of membranes from poly(styrene-alt-maleic acid) (PSaMA) with a focus on acid concentration in the coagulation bath, and polymer and additive concentration in the casting solution. Nanofiltration membranes are prepared using significantly lower concentrations of acid: 0.3 M HCl compared to the 2 M of either acetic or phosphoric acid used in previous works. It is shown that higher polymer concentrations can be used to prevent defect formation in the top layer. In addition, acetic acid concentration also strongly affects casting solution viscosity and thus can be used to control membrane structure, where lower acetic acid concentrations can prevent the formation of macrovoids in the support structure. The prepared nanofiltration membranes exhibit a very low molecular weight cutoff (210 ± 40 dalton), making these sustainable membranes very relevant for the removal of contaminants of emerging concern. Understanding how the parameters described here affect membrane preparation and performance is essential to optimizing membranes prepared with APS towards this important application.

Amine–carbon quantum dots (CQDs–NH2) tailored polymeric loose nanofiltration membrane for precise molecular separation

Nanofiltration membranes show great potential in water treatment and resource recovery for their special separation mechanisms that can separate the small molecules effectively. However, their wide application needs to address the low separation efficiency caused by the similar solute sizes and charges while using the charged NF membranes with nanopores. This work reports a low-cost amine–carbon quantum dots (CQDs–NH2) modified thin-film composite (CTFC) membrane via the facile interfacial polymerization process. The electrostatic force and competing reaction between the positively charged CQDs–NH2 and the reactive monomers reformulated the interfacial polymerization process. The resultant CTFC membrane exhibits improved surface morphology and hydrophilicity. Besides, the incorporation of CQDs–NH2 changed the original polyamide network structures to construct more transport space. The CTFC membrane permeance was boosted significantly (from 6.2 to 38.44 L m−2 h−1 bar−1) compared with the unmodified TFC membrane, showing precise dyes separation property. This work may offer valuable guidance for the low-cost loose nanofiltration membrane preparation towards molecular separation.

Epoxy-based solvent-tolerant nanofiltration membranes prepared via non-solvent induced phase inversion as novel class of stable membranes

A novel synthesis method of partially crosslinking a polymer solution prior to casting, has been successfully developed for the preparation of solvent-tolerant nanofiltration (STNF) membranes. STNF merges solvent resistant nanofiltration (SRNF) with aqueous nanofiltration. The feed solution consists of a mixture of solvent(s) and water, requiring a membrane with both high water permeability and solvent stability. In this work, epoxy resins are proposed to meet these requirements. The well-known epoxy curing bulk chemistry via ring-opening reactions has been applied followed by a phase inversion process, to form membranes with intermediate polarity, excellent stability and permeability, making them particularly suitable for the treatment of solvent/water mixtures.Several epoxy monomers were screened, based on size and number of epoxide functional groups. Different amines with varying length and reactivity were chosen as curing agent. Both reagents were dissolved in dimethyl sulfoxide (DMSO) and left to react. The increasing solution viscosity was monitored as a function of time and related to the reaction rate of the epoxy-amine curing system. Integrally skinned asymmetric membranes were prepared via non-solvent induced phase inversion. Filtration experiments were carried out in 20/80 dimethyl formamide (DMF)/water mixtures with Rose Bengal (RB, 1018 g mol−1), Rhodamine 6G (R6G, 479 g mol−1) and Methyl Orange (MO, 327 g mol−1) as solutes.A blend of 2 epoxides, i.e. EPON 1009F (20 wt%) and EPON SU-8 (10 wt%), in DMSO resulted in RB retention of 99+ % and a R6G retention of 77% in DMF/water with a permeance of 0.75 Lm−2h−1bar−1. Addition of tetrahydrofuran (THF) as co-solvent (5/1, DMSO/THF) increased the selectivity further towards a 99% RB and R6G retention and an 85% MO retention with a permeance of 0.29 Lm−2h−1bar−1. ATR-FTIR spectra indicated that the membranes are stable after immersion of 5 days in very harsh conditions, i.e. pH = 0–14, and in a variety of solvents.

Construction of a gelatin scaffold with water channels for preparing a high performance nanofiltration membrane

In order to realize energy saving and resource recovery in desalination and waste-water treatment, it is urgent to develop nanofiltration (NF) membranes with high permeability and selectivity. Therefore, many researchers devote to designing different hydrophilic polymer-interlayers for the thin-film composite (TFC) membranes, targeting to prepare NF membranes with outstanding separation performance. However, the thin polymer-interlayer (<10 nm) can only slow down the diffusion rate of aqueous monomer and affect the interfacial polymerization (IP) process, forming a thin and defect-free polyamide (PA) layer. Herein, we constructed a hydrophilic and homogeneous gelatin (GT) scaffold with a thickness of over 100 nm on polysulfone (PSF) substrate and prepared a PA separation layer by IP process to obtain a high-performance TFC based NF membrane. The scaffold can not only affect the diffusion rate of piperazing (PIP) in IP process to form a thin PA layer, but also provide additional channels for water diffusion, which would significantly improve the permeability of NF membranes. Moreover, the fabricated PA layer has a high cross-linking degree and a negative surface potential, endowing the NF membrane with a high salts rejection rate, especially for divalent anions. Hence the permeability of the resulting NF membrane (up to 16.95 ± 1.18 L m−2 h−1 bar−1) is about 2.5 times as compared with the controlled membrane, while achieving a high Na2SO4 rejection of 99.3% ± 0.2%. In addition, the coefficient of selectivity for NF membrane are 97.73 for αNaCl/Na2SO4 and 45.66 for αNaCl/MgSO4 respectively, which are several times higher than those of the controlled NF membrane. This work provides a low-cost and facile method to prepare a TFC based NF membrane with a high permeability and selectivity.

Hybridly charged NF membranes with MOF incorporated for removing low-concentration surfactants

Water pollution is a growing issue that requires remediation. Surfactants, used in many domestic and industrial applications, are one of the emerging contaminants that require immediate concern. Removing low-concentration surfactants using nanofiltration (NF) membrane is a study that deserves attention. In this case, a mixed polyamide-based NF membrane was fabricated via interfacial polymerization (IP) using polyethylenimine (PEI) and piperazine (PIP) as monomers in aqueous solution. UiO66-NH2 and UiO66 were synthesized and incorporated into the polyamide layer to enhance the permeability of the prepared NF membranes. The pure water flux of the NF membranes reached 16.6 L m−2 h−1 bar−1 when UiO66-NH2 concentration in aqueous solution is 0.005 wt%, and the membrane showed decent rejection to divalent salts, 96.5% to MgCl2 and 85.6% to Na2SO4. The prepared membranes were utilized to remove surfactants with the concentration (100 mg L−1) below the critical micelle concentration (CMC) from water, and they showed good removal to both anionic and cationic surfactants. In addition, the durability of the fabricated NF membranes is acceptable. This work provides a feasible strategy for the fabrication of highly permeable NF membranes and demonstrates the capability of NF membrane for surfactants removal.

Enhancing the performance of TFC nanofiltration membranes by adding organic acids in polysulfone support layer

Throughout this study, the effect of certain organic acids, methacrylic acid, lactic acid and tartaric acid, doped in polysulfone (PSF) casting solution onto the performance of nanofiltration (NF) membranes was investigated. Different NF membranes have been prepared from m-phenylenediamine and trimesoylchloride onto the top surface of the acid-modified PSF membranes through regulating the concentration and contact time of the conventional interfacial polymerization process. The study of scanning electron microscopy (SEM) was used to investigate the influence of acids on the morphology of membranes and cross-sectional structures. The functional groups, hydroxyl and carboxylic acid, of the acids have resulted in a significant increase in membrane thickness, porosity and hydrophilicity, with a decrease in macrovoid capacity of the PSF layer. The acid-modified PSF/TFC membranes showed higher rejection of salt, with an increment in water flux compared to the neat membrane. Water flux and salt rejection (Rs %) of the control membrane was 7.6 L/m2 h and 65.4%, whereas polysulfone/methacrylic acid (PSF/MAAc), polysulfone/tartaric acid (PSF/TAc), and polysulfone/lactic acid (PSF/LAc) were 16.8, 18.5, and 20.2 L/m2 h and 88, 88.2 and 94.1%, respectively. Efficiency of prepared NF membranes under various inlet pressures and specific salts was investigated with selectivity and salt rejection. The salt rejection of a mixed salt solution was found to meet the order of Rs % CaSO4 ≥ Rs % Na2SO4 ˃ Rs % MgSO4 ˃ Rs MgCl2 ˃ Rs % NaCl.

Rapid preparation of Tannic acid (TA) based zwitterionic nanofiltration membrane via a multiple layer-by-layer (mLBL) assembly strategy for enhanced antifouling performance

Tannic acid (TA) is a promising material to prepare nanofiltration membranes due to its multiple interaction abilities with metal ions and zwitterionic polymer via coordination interaction and electrostatic interaction, respectively. Herein, we proposed a multiple layer-by-layer (mLBL) assembly strategy using three assembly materials for the rapid preparation of TA based zwitterionic nanofiltration membranes with enhanced antifouling performance, which was compared with the non-zwitterionic nanofiltration membranes prepared via the conventional layer-by-layer (cLBL) assembly. Among a series of transition metal ions, Fe3+ was chosen to prepare nanofiltration membranes. The ATR-FTIR and XPS analysis revealed the TA/Fe3+ layer was formed and the poly(sulfobetaine methacrylate) (PSBMA) polymer was successfully assembled on membrane surface. The prepared zwitterionic nanofiltration membranes showed enhanced hydrophilicity, roughness and zeta potential than the non-zwitterionic nanofiltration membranes. The influence of TA/Fe3+ bilayer number and PSBMA concentration on membrane performance was systematically studied and the rejection properties of the prepared membranes for dyes and salts were also investigated. Under the optimum preparation condition, the zwitterionic (TA/Fe3+)1.5/PSBMA membrane showed water permeability of 40.36 LMH/bar with rose bengal (RB) rejection more than 98% and Na2SO4 rejection about 60%. Because of the introduction of the PSBMA polymer, the zwitterionic (TA/Fe3+)1.5/PSBMA membrane showed better antifouling performance than non-zwitterionic (TA/Fe3+)2.5 membrane with similar rejection properties.

Cefalexin crystallization residual liquor separation via nanofiltration based multistage process

Pharmaceuticals manufacture is of importance to human life and health. Great amount of pharmaceuticals crystallization residual liquor was produced in the pharmaceuticals manufacture, which lead to adverse influence on the green chemical engineering and environment. Herein, we proposed a multistage separation process based on nanofiltration technology to recover cefalexin crystallization residual liquor separation. The influence of membranes, pH value, concentration as well as separation stages on the separation performance was explored. The nanofiltration membrane (NF-200D) with strong electronegative charge showed a high rejection of 74.00% for 7-amino-3-desacetoxycephalosporanic acid (7-ADCA) and low rejection of 7.06% for D-phenylglycine in mixed solution. The increase in the electronegative charge of NF membranes could enhance the repulsion between membrane and solute molecules. The separation factor of nanofiltration membrane for 7-ADCA and D-phenylglycine reached a peak value of 3.06 at pH 8.0 and concentration of 10 mmol L−1. Using three stage separation, the concentrated 7-ADCA (C7-ADCA = 23.12 g L−1) and the permeate D-phenylglycine (CD-phenylglycine = 0.19 g L−1) were obtained. Further improved separation sequence should focus on the preparation of nanofiltration membranes with strong electronegative charge and acid-base tolerance, and the nanofiltration process design with enhanced efficiency of separation process.

Preparation and properties of hollow fibre nanofiltration membrane with continuous coffee-ring structure

Polyamide (PA) hollow fibre composite nanofiltration (NF) membranes with a coffee-ring structure and beneficial properties were prepared by adding graphene oxide (GO) into the interfacial polymerization process. The presentation of the coffee-ring structure was attributed to the heterogeneous, finely dispersed multiphase reaction system and the “coffee-stain” effect of the GO solution. When the piperazine concentration was 0.4 wt-%, the trimesoyl chloride concentration was 0.3 wt-%, and the GO concentration was 0.025 wt-%, the prepared NF membranes showed the best separation properties. The permeate flux was 76 L·m−2·h−1, and the rejection rate for MgSO4 was 98.6% at 0.4 MPa. Scanning electron microscopy, atomic force microscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy were used to characterize the chemical structure and morphology of the PA/GO NF membrane. The results showed that GO was successfully entrapped into the PA functional layer. Under neutral operating conditions, the PA/GO membrane showed typical negatively charged NF membrane separation characteristics, and the rejection rate decreased in the order of Na2SO4 > MgSO4 > MgCl2 > NaCl. The PA/GO NF membrane showed better antifouling performance than the PA membrane.

High performance nanofiltration membrane based on SMA-PEI cross-linked coating for dye/salt separation

Construction of high performance nanofiltration (NF) membrane is of critical importance in dye desalination. In this paper, a novel composite NF membrane with good dye/salt separation performance was prepared via blending and crosslinking method. Firstly, the membrane matrix was prepared by blending styrene-maleic anhydride (SMA) with polyether sulfone (PES) via non-solvent induced phase separation (NIPS), then polyethylenimine (PEI) was introduced on the membrane surface by crosslinking reaction with SMA. Single component filtration tests of the prepared NF membrane showed that the rejection of the dye with the molecular weight greater than 696 Da reached more than 99% and the membrane possessed high flux of above 23 L/m2 h bar. The separation tests of Congo red and NaCl mixed solution at optimized conditions exhibited 99.4% rejection for Congo, and 2.5% rejection for NaCl, moreover, the separation performance remained stable in the test run for 36 h. All these indicate that the prepared NF membrane can be applied to dye desalination.

Electrospun Keratin-Polysulfone Blend Membranes for Treatment of Tannery Effluents

Due to the high toxicity of effluents radiating from tannery industries, there is a need for effluent treatment so as to limit its dangerous impacts on the environment. Fabricating responsive membranes is gaining significant interest in wastewater treatment applications. This study investigates the preparation, characterization, permeation, and antifouling properties of the keratin-polysulfone blend membranes. Keratin, a bioinspired material, is used as the responsive element along with the polysulfone matrix, which together acts as the responsive membranes for efficient filtration. Keratin was extracted from the goat hair, a tannery waste, through ball milling—an ecological, cost-effective, and time-consuming method. Keratin-polysulfone was blended in the ratio 95:5 (v/v) in their respective solvents to prepare nanofiltration membranes. The morphology of the membranes shows the random arrangement of fibers with the interstitial spaces. Contact angle measurements reveal that the keratin-polysulfone blend membranes are partially hydrophilic, which in turn resulted in good antifouling properties. Improved porosity of the fabricated membranes enabled good absorption capacity, and enhanced mechanical properties are an added advantage for the fabricated membranes. Since the membrane showed enhanced filtration property, the post-tanning effluents from the leather industry have been treated by the keratin-polysulfone fabricated membranes. The treated effluent showed a maximum percentage reduction in chemical oxygen demand (COD) and biological oxygen demand (BOD) concentrations of about 53% and 66%, respectively. The dye removal efficiency of the fabricated membrane is reported to be 76%. Thus, filtration efficiency has been established paving a way for treating effluents in an efficient way.

Preparation of graphene oxide/silica hybrid composite membranes and performance studies in water treatment

Water shortages have become a major problem facing the world today. Membrane separation technology is commonly used in water treatment applications. The development of new materials for water treatment can reduce the energy required for water treatment, reduce cost, and improve efficiency. The unique structure and properties of graphene and silica make them attractive materials for preparation of nanofiltration membranes for water treatment. We have successfully prepared a graphene oxide/silica (GO/SiO2) hybrid composite materials by in situ hydrolysis, using tetraethyl orthosilicate (TEOS) as a silicon source in an alkaline environment. The chemistry and structure of these materials are characterized by TEM, FTIR, Raman, and XPS of GO and the GO/SiO2 composite. BET porosimetry reveals that the total pore volume of the composite is 2.84 cm3 g−1, the specific surface area is 2897 m2 g−1, and the average pore diameter is 3.97 nm. We prepared GO membranes and GO/SiO2 composite membranes by vacuum suction filtration. The morphology of the membrane was observed by FESEM and AFM. The composite membrane has a larger surface roughness (Rms = 9.39). We also tested the thermal stability by TGA, and hydrophilicity by water contact angle measurements. The water permeance of the composite membrane is up to 229.15 L m−2 h−1 bar−1, and the rejection of the rhodamine B dye molecules is as high as 99%. The GO/SiO2 hybrid composite membrane has good hydrophilicity and thermal stability, high water permeance and rejection, and can be developed as a high-performance material for water treatment.

Oleic acid-functionalized TiO2 nanoparticles for fabrication of PES-based nanofiltration membranes

In this study, hybrid nanofiltration (NF) membranes were fabricated by introducing oleic acid-titanium oxide (OA-TiO2) nanoparticles into the polyethersulfone (PES) by phase inversion method. The OA-TiO2 nanoparticles were synthesized and then different concentrations of synthesized nanoparticles were used to prepare NF membranes. The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), and X-Ray Diffraction analysis (XRD). Moreover, the morphology of membranes was investigated by FESEM, the energy dispersive X-ray (EDX) analytical method, atomic force microscope (AFM) analysis. The separation performance of membranes was evaluated by the contact angle, pure water flux (PWF), flux recovery ratio (FRR%), and the rejection of Na2SO4 and Cu(NO3)2. The highest PWF (18.206 L/m2h) was obtained to PES-based membrane containing of 0.05 wt.% OA-TiO2 nanoparticles with a 42% increase compared with the pristine PES membrane at operating pressure of 4.5 bar due to increasing membrane hydrophilicity and better dispersion of OA-TiO2 nanoparticles. Furthermore, the best Na2SO4 rejection (81.5%) was obtained to membrane containing of 0.1 wt.% of OA-TiO2 nanoparticles and the highest Cu(NO3)2 removal (79%) was revealed to membranes containing of 0.5 wt.% OA-TiO2 nanoparticles that showed the increase of 21% and 25% compared to the pristine PES, respectively. The enhancement of salt rejection attributed to electrostatic repulsion and adsorption mechanisms. The incorporation of OA-TiO2 nanoparticles into the PES enhance FRR% to 83% that led to improving anti-fouling properties.

Preparation of internally pressurized polyamide thin-film composite hollow fiber nanofiltration membrane with high ions selectivity by a facile coating method

Internally pressurized polyamide thin-film composite (TFC) hollow fiber nanofiltration (NF) membrane with high ions selectivity was prepared by a facile coating method including the dip-coating of the aqueous phase and reverse direction coating of organic phase. Surface composition and morphologies of the prepared NF membrane were characterized by ATR-FTIR, FESEM and AFM. Membrane hydrophilicity was evaluated by Water Contact Angle (WCA) measurements. The dip-coating time of the aqueous phase and reverse direction coating time of organic phase were optimized. The results indicated that the ultra-thin functional layer was successfully formed on the lumen side of hollow fiber PSF substrate membrane. Under the optimized conditions including the dip-coating time of 20 min and reverse direction coating time of 60 s, the prepared TFC hollow fiber NF membrane exhibited an excellent separation performance with the 99.5 % rejection of MgSO4 (1 g/L) and pure water flux of 43.3 L/m2h at 0.7 MPa. The prepared NF membrane showed a high selectivity with the separation factor of MgSO4/NaCl) of 7.8. NF membrane exhibited a uniform separation performance along fiber length compared with the traditional single direction coating.

Development of nanofiltration membranes using mussel-inspired sulfonated dopamine for interfacial polymerization

A mussel-inspired sulfonated dopamine (SDA) was synthesized and used as an aqueous monomer to cross-link with trimesoyl chloride (TMC) via interfacial polymerization to prepare nanofiltration membranes. The sulfonic acid groups of SDA were credited with the enhancement of membrane performance, as a result of restraining the process of interfacial polymerization and oxidative-polymerization. Moreover, it also endowed these nanofiltration membranes with more hydrophilic, negatively-charged and smoother surfaces. The optimized nanofiltration membranes (NF-SDA-0.1) exhibited a water flux as high as 62.2 L∙m−2∙h−1 (0.6 MPa), while maintained applicable salt rejection of Na2SO4 (~90.0%) and dye rejections of Congo red, Methyl blue, Methylene blue and Brilliant green (all >99.9%). Thus, the sulfonated dopamine was considered as a promising candidate as aqueous phase monomer for the preparation of high-performance nanofiltration membranes.